Electric furnace.



W. N. CRAFTS. ELECTRIC FURNACE. APPLICATION FILED NOV. 28, 1911.

1,1 14,733, I PatentedOct-QF, 1914.

2 SHEETSSHEET l,

I HT'I RNEA W. N. CRAFTS.

ELECTRIC FURNACE.

APPLICATION FILED NOV. 28, 1911.

1,1 14,733. Patented 00c. 27, 1914 2 sums-511mm.

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WALTER N. CRAFTS, OF OBEB-LIN, OHIO.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented Oct. 27, 1914.

Application filed November 28, 1911. Serial N o. 662,822.

useful Improvement in Electric Furnaces.

of which the following is a full, clear, and

exact description, referenoebeing had to the accompanying drawings.

This invention relates to electric furnaces of the induction type. In such furnaces it has been customary to provide an induction coil, the primary of which carries alternat ing current and the secondary of which consists of an annular horizontal bath of-the material to be fused. In such furnaces thebath is'of inconvenient restricted form; the capacity is limited; it is diflicult to work the furnace and to obtain proper circulation of the metal being fused; there is a large sur face exposed to scorification, and repairs are difiicult. Another disadvantage is the comparatively low power factor, due 'to the dis tance between the primar winding and the secondary, which is necessary on account of the heat ofthe secondary.

The object of my invention is to obviate these difficulties and produce an electric induction furnace of large capacity, with an unrestricted bath, easily worked and repaired, and having a high power factor.

In accomplishing this I provide a secondary circuit consisting only partly of fusible material within the bath, the remainder beingoutside of the bath and made of highly con ductive material, which will not'fuse in the operation of the furnace. To this end I make the external portion of the conductor of greater conductivity than; the bath, so that the current does not heat-it to the fus ing point.

My invention comprises such a furnace broadly considered and also the more particular embodiment thereof illustrated in the drawings and hereinafter described.

In the drawings, Figure 1 is a side ele vation of an open hearth furnace of the cradle type, embodying my invention; Fig. 2 is a vertical section of the same; Figs. 3

and 4 are horizontal sections, respectively,

through the bath and the cores of the in ductiondevice; and Fig. 5 is a vertical section through one of the cores,the planes respondingly numbered lines in Fig. 2.

In the drawings, 10 representsthe furnace body, which is of suitable refractory material (as magnesite, for example) surrounded by the metallic shell 11 and provided with an arched roof 12. 13 designates the basin of this furnace, which is shown as carryingan open bath 14. Above the top line of the bath are the charging openings 15 and 16 on the end and sides of the furnace, these openings being adapted to be closed by suitable doors l7 and 18.

19 indicates the pouring spout connecting through the tap opening 20 with the chamber normally above the bath.

The body above described is shown as mounted on cradles 25, which rest on rollers '26 on suitable supports 27. This enables the furnace to be tipped, as desired, to pour the molten metal through the opening 20.

30 indicates two magnetic cores of the induction device. These cores are of laminated form and mounted horizontally below the furnace body and connected at their ends by yokes 31. As shown, the cores are sup ported by having their yokes 31. rest on brackets 32 secured to the cradle. As shown, these brackets are insulated from the cradle, being mounted with interposed insulation 33.

35 indicates the the cores 30. Y

36 indicates a metal member which lies beneath and onto the two opposite sides of the primary windings and extends up into the furnace body so that its upper ends are in contact with the bath 14. This metal member 36 is shown as of a double or multiple U- shape to accomplish this result, having a leg 37 on the outer side of each coil and a leg 38 of double width between the two coils. This member 36 is shown asresting on the insulation 33. With the conducting material in the bath, it constitutes two annular secondaries of the induction coil. Now when an alternating current passes through the primary winding, the two annular secondaries, including the solid metal member 36 and the material in the bath between the upper ends of the legs, becomes heated. By making the member 36 of a material which is of higher conductivity than the material in the bath between the legs, I am enabled to fuse the bath without fusing this external portion of the secondary. For example, if the'external secondary member 36 be made of copper, its electric resistance may be many times less than that of the material of the bath between the unner ends primary winding about of the copper legs, with the result that there may be an induced current suflicient to fuse the bath without fusing or even unduly heating the external portion of the secondary. The external portion of the secondary "below the furnace body may be exposed to the air'and thus'ventilate and cool itself by radiation. The portions of the legs 37 and 38 within the bottom of the body I prefer to cool artificially. For this purpose I have shown each of these legs as enlarged where they pass through the body and having embedded within them coils 40 through which a cooling liquid may pass. I have shown these coils all connected at one end'with acommon pipe 41 and at the other end with a common pipe 42, one of these pipes being an intake pipe and the other the exit for the cooling liquid.

indicates suitable plates in the walls of the furnace on opposite sides of the bath,

which. are terminals of branches of either theprilnary or secondary circuit, orother- Wise supplied with current, and may operate to heat the bath and slag by resistance. It is to be understoodthat the width of the bath is properly selected so that the desired resistance to the passage of current is obtained.

In starting my furnace, either molten metal or finely divided metal, such as drillings or turnings, is placed in the bath sufficiently to bridge the distance between the legs 37 and 38 of the external secondary, and the current through the primary is started. This establishes a current through the exposed portion of the secondary and the internal portion bridging between the legs, and this fuses the internal portion .without unduly heating the external portion. Additional material to be reduced, melted or refined is supplied from time to time to the bath through the doors, until the bath is completely melted and refined to the desired extent, when the furnace tipped to discharge the contents in the usual I manner.

former core and primar windings may be used in a newly repaire furnace, while the old body is being repaired. The entire slag line can be repaired while the furnace is hot. Another advantage is that, with my furnace, the largest part of the heat is produced above the magnet and primary winding, so that they do not suffer from the effects of the heat, nor is cumbersome ventilation of them necessary. Because the copper legs forming the outside portion of the secondary are cool they can be placed very close to the primary, thus producing a very.

high power factor. The greatest heat .is

' produced at the bottom of the hearth and hence better circulation of the molten metal is obtained, aswell as, a great reduction in the loss from radiation. With my type of furnace, banks and roof can be made very high to. permit a great amount of slag and foaming, which occur in those processes of refining steel where a large per cent. of ore is used.- With my furnace, there is an entire freedom from electrode troubles, as well as the saving-in the cost of electrodes, as compared with the arc type of furnace.

Changes and alterations may be made in the construction and arrangement of the parts shown, as willv be readily understood. Making the external solid secondary in the double U-shaped form is effective and satisfactory for either single phase or two phase current. Where'three phase current is used this multiple member preferably has an additional intermediate leg of the same character as the intermediate leg shown. I have mentioned making this external U-shaped member of copper, though it is to be understood that other metals of relatively high conductivity may be employed, if deslred.

Having thus described my invention,what I claim is:

1. In an electric furnace, the combination, witha basin, of an induction coil having an incompletely annular solid secondary portion exterior of and below the basin cooperating with a bottom portion of the bath in thebasin tomake a completely annular secondary. l

2. In an electric furnace, the combination, with a basin, of an induction coil having an unfused incomplete secondary exterior of the basin and terminating at the'bottom of the basin and adapted to be completed by fused material within the basin.

3. In an electric furnace, the combination, with a basin, of a magnetic core, a primary winding, and an unfused incomplete secondary having terminals at the bottom of the basin and adapted to be completed by means of a portion of the bath within the basin.

4. In an electric furnace, the combination, with a basin, of a magnetic core outside of the basin, a primary winding, and an incomplete secondary having terminals at the bottom of the basin and adapted to be completed by means of a portion of the bath :within the basin, saidsecondary exterior of the basin being of material of relatively '60. on such core.

' high conductivity and hence remaining un-' ductor extending about such winding and passing through the bottom of the furnace body and terminating adjacent to the bottom of the basin, said U-shaped member being of relatively high conductivity as compared with the material in the basin.

7. In a electric furnace, the combination of a furnace body having a basin, a U- shaped metallic member of relatively high conductivity beneath the basin and having its upper end extending through the body into position'adjacent to the bottom of the bath, a core, and primary winding about the core between the legs of such member.

8. The combination, with a furnace basin,

of a U-shaped solid metal member exterior of the basin and having its ends terminating at the bottom of the basin, and a primarywinding located in proximityto such U-shaped member, the U-shaped member and fusible material within the basin form ing an annular secondary.

9. In an electric furnace, the combination, with a furnace basin, of a core and primary winding, and a solid U-shaped conductor extending about such winding and passing through the furnace bodyinto electric contact with the bottom of the bath, said conductor exterior of the body being exposed for cooling by radiation.

10.'The combination, with a furnace basin, of a U-shaped metal member exterior -of the basin and having its ends terminatin the operation of the furnace,'a core eX-. tending transversely between the legs of the gu-shaped member, and a primary winding 12. The combinatiomwith a furnace body 'having a basin, of a metal member made in a U-shape and having its legs extending through the bottom of the furnace body into 6? electric connection with the basin contents,

ing at the bottom of the basin, a' primary winding located in proximity to such U bottom of the body, said member being of meansfor cooling such legs where they pass through the body, a horizontal core beneath the body and between the legs, and a primary winding on such core.

'13. The combination of a furnace body having a basin, a metal member made in double-U-shape having three solid extending legs terminating within the furnace basin, magneticcores on opposite sides of the central leg of said member, and primary windings on such cores occupying the two U- portions of the member.

14. The combination, with a furnace basin, of a double U-shaped solid metal member exterior of the basin and having its ends terminating at the basin,an annular magnetic member occupying the two bends of the member first mentioned, and a primary winding about such magnetic member.

15..lhe combination of a furnace body having a basin, a solid metal member made in double-U-shape having three extending legs terminating within the furnace basin,

magnetic cores on op )osite sides of the central leg of said'm'em er, primary windings on such .cores occupying the two U-portions ,of the member, and means for cooling the metal legs within the furnace body.

16. The combination, with a furnace body having a basin, a solid U -shaped metal memberhaving its legs embedded in the furnace body, the upper ends of the legs being exposed-at the bottom of the basin, cooling coils within such legs in the body, a transverse core between the legs, and a primary winding around such core.

17. In an electric furnace, the combination, with a body, of a support therefor on which the body removably rests, a solid-U- shaped metal member carried by the body and depending from it, the legs of the U terminating within the basin carried by the body, a transverse core beneath the body, and a primary winding for said core.

18. In an electric furnace, the combination .of a body having a basin, an incompletely annular copper member having solid legs terminating adjacent to the bottom of the basin, said member with fusible mater'ial in the basin constituting an annular conductor, and primary winding making an induction coil with such annular conductor.

19. The combination, with a furnace body having a basin, 0'? a multiple U -shaped member beneath the body having legs extending through the bottom of the body into electric connection with the basin contents, cores beneath the body lying between the legs,

ber beneath the body having legs extending connection with the basin contents, cores beneath the body lying between the legs, primary windings around such cores, the legs being enlarged where they extend through the body, and cooling coils embedded in such legs.

21. The combination, with a furnace body having a basin, of a multiple U-shaped solid member of relatively high conductivity depending from the body and having its surface exposed for radiation, and having legs extending through the bottom of the body into electric connection with the basin con- .tents, and cores and primary windings beneath the body lying between the legs, the outer legs being of less cross section than the intermediate leg or. legs and the legs being internally cooled where they pass through the furnace body. 22. The combination, with a furnacebasin, of an induction coil having a core, a primary winding and an annular secondary located in an up and down plane and consisting of a. portion of a continuous molten bath in the bottom portion of the basin, and a con: tinuous solid conductor terminating at its upper end at the bottom of said bath.

In testimony whereof, I hereunto my signature in the presence of two witnesses.

. WVALTER N. CRAFTS. l/Vitnesses:

ALBERT H. BATES, BRENNAN B. WEST. 

